1. Field of the Invention
The present invention relates to a charger that charges a plurality of batteries all at a time, or more specifically, a charger that charges, for example, a multi-parallel battery pack.
2. Description of the Related Art
A common charger that charges a multi-parallel battery pack consisting of a plurality of battery banks is one that finishes the charging at the time point when any one of the battery banks is fully charged, regardless of whether or not the other battery banks are fully charged. At the start of charging, battery banks usually have different state of charge. After any one of the battery banks is fully charged, if the charging is continued until all the other battery banks are fully charged, the first fully charged battery bank will be overcharged and might be deteriorated. For this reason, there is high possibility that a multi-parallel battery pack that is charged by a conventional charger mixedly contains the battery bank fully charged and those not fully charged, or that the state of charge of the battery banks becomes imbalanced. It is then likely that the primary overall battery capacity cannot be retained.
Among other conventional technologies of charging a multi-parallel battery pack consisting of a plurality of battery banks, a well-known technology is, for example, a charging method that repeatedly charges each battery bank in a multi-parallel battery pack consisting of a plurality of battery banks for a short period of time with an adequately low charging current (See Unexamined Japanese Patent Publication (Kokai) No. 2008-259260).
The imbalance of state of charge of the battery banks in the multi-parallel battery pack can be solved, for example, by detecting a state of full charge of each battery bank and finishing the charging of the battery banks one by one. On the other hand, in order to detect the state of full charge of each battery bank and finish charging the battery banks one by one, it is required to implement charge control on each battery bank. This might complicate the procedure of the control. If the state of full charge is detected with respect to each of the battery banks, and the charging is finished one by one, since the conditions of the battery banks are imbalanced during the charging, there is the possibility that the state of full charge of the battery banks cannot be accurately detected due to interaction of the heat generated in the battery banks.
The conventional technology disclosed in Unexamined Japanese Patent Publication No. 2008-259260 does not solve the imbalance of state of charge of the battery banks unless the state of charge of the battery banks are the same when the charging begins. According to the conventional technology disclosed in Unexamined Japanese Patent Publication No. 2008-259260, the battery banks are basically not fully charged, so that there still is the possibility that the primary battery capacity of the multi-parallel battery pack cannot be retained.